I've "fixed" it over 5 times now. First, replaced the gasket. Then filed the (aluminum) housing flat, it was pitted. Plus another new gasket. Then a new gasket and sealer. Then a steel thermostat housing I had, plus new gasket with sealer. Most recently, a near mint condition steel housing with a gasket, no rtv this time (I guess the ridge on the housing wasn't enough), and it still leaks. Every single part in the cooling system is new, engine is freshly rebuilt last year. This just started happening this month. Was fine for the past year. And the temp gauge will wander from what I think is 210ish back to ~190 (195* stat, which I also changed), over the course of a minute it will do it 3 or 4 times. It's in my '85 Regal with a '70 SP 350. What puzzles me the most, is this just started out of the blue. no warning, nothing. And what infuriates me the most, is nothing I have tried has worked. It will be fine for a day, at most 2, then start leaking again. It is seemingly leaking from the bottom portion of the gasket, I can never see any droplets running down the sides or the top. There is no spray, no dribbles. It also only does it after the car is shut off after being at temp. Temp peaks at 230 when off then comes back down normally.